Biometric authentication apparatus and biometric authentication method

ABSTRACT

A biometric authentication apparatus includes: a storage unit which stores representative matching data representing features of biometric information of a registered user and representing conditions of a designated body part of the registered user, each representing one of at least two different portions of a variation range over which the condition of the body part containing the registered user&#39;s biometric information varies due to cyclic environmental variations; a biometric information acquiring unit which generates a biometric image representing biometric information of a user; a matching data generating unit which generates, from the biometric image, input matching data that represents the features of the biometric information of the user; a matching unit which matches the input matching data against at least one of the representative matching data; and an authentication judging unit which judges, based on a result of the matching, whether the user is to be authenticated or not.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2012-249203, filed on Nov. 13,2012, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are related to a biometricauthentication apparatus and a biometric authentication method.

BACKGROUND

Recent years have seen the development of biometric authenticationtechnology for authenticating a user of an apparatus or system based ona biometric image representing the user's biometric information such asa palm or finger vein pattern or a fingerprint or palm print. Abiometric authentication apparatus using such biometric authenticationtechnology acquires, for example, as an input biometric image, abiometric image representing the biometric information of the user whois going to use the biometric authentication apparatus. Then, thebiometric authentication apparatus compares input biometric information,i.e., the user's biometric information represented on the inputbiometric image, with preregistered biometric information, i.e., thebiometric information prestored in the form of a biometric image foreach preregistered user. If the result of the comparison indicates thatthe input biometric information matches the preregistered biometricinformation, the biometric authentication apparatus authenticates theuser as being a legitimate registered user. The biometric authenticationapparatus then permits the authenticated user to use the apparatus inwhich the biometric authentication apparatus is incorporated or someother apparatus connected to the biometric authentication apparatus.

The biometric information represented on such a biometric image changesdepending on the condition at the time of acquisition of the biometricimage. For example, when a palm vein pattern is used for authentication,the condition at the time of biometric image acquisition that affectsthe biometric information includes the orientation of the hand such asthe position or tilting of the hand relative to the vein sensor. On theother hand, when a fingerprint is used for authentication, the conditionat the time of biometric image acquisition that affects the biometricinformation includes the orientation of the finger relative to anarea-type fingerprint sensor or the moving speed of the finger relativeto a slide-type fingerprint sensor. If the change in the biometricinformation is large enough that the difference between the inputbiometric information represented on the input biometric image and thepreregistered biometric information represented on the biometric imageacquired at the time of registration becomes significant, theauthentication accuracy may degrade. In view of this, the biometricauthentication apparatus, for example, determines whether the conditionat the time of acquisition of the biometric image is appropriate or not,and if it is determined that the condition is not appropriate, an imageof the biometric pattern is recaptured to reacquire the biometric image,and the reacquired biometric image is used for authentication, therebypreventing the degradation of the authentication accuracy.

The biometric information represented on the biometric image may alsochange when the condition of the body part containing the biometricinformation is affected, for example, by an environmental factor such asweather. When a palm vein pattern is used for authentication, thecondition of the body part is, for example, the degree of contraction ofthe blood vessels due to temperature. On the other hand, when afingerprint is used for authentication, the condition of the body partis, for example, the skin condition which depends on the degree ofdryness of the skin surface due to humidity. For most users, thecondition of the body part containing the biometric information isrelatively unaffected by temperature or humidity variations associatedwith seasonal variations; therefore, for such users, the authenticationaccuracy is stable throughout the year.

On the other hand, for some users, the condition of the body partcontaining the biometric information may be significantly affected bytemperature or humidity variations associated with seasonal variations.For such users, if the biometric information is registered, for example,in summer, the input biometric information represented on the inputbiometric image acquired in winter for authentication may besignificantly different from the registered biometric information, andthe biometric authentication apparatus may fail to authenticate theuser.

In the prior art, methods are proposed for updating the registeredbiometric information as needed (for example, refer to JapaneseLaid-open Patent Publication Nos. 2007-226519, 2010-61528, 2006-85268,2010-79448, and 2008-171094). For example, in Japanese Laid-open PatentPublication No. 2007-226519, there is proposed a biometric informationupdating management system in which, if the last update date of themaster biometric information stored in a storage device is past itsvalidity date, the biometric information presented for authenticationand judged to match the master biometric information is registered asthe master biometric information. On the other hand, in JapaneseLaid-open Patent Publication No. 2010-61528, there is disclosed abiometric authentication apparatus in which feature information havinghigh reproducibility is extracted from the registered data and the datapresented for authentication, and new registration data is created fromthe extracted feature information and is used to update the registereddata.

Further, in Japanese Laid-open Patent Publication No. 2006-85268, thereis proposed a biometric authentication system in which when theperformance of authentication using the registered data stored in an ICcard registration data storage unit has degraded, the registered datastored in the registration data storage unit is updated by registereddata stored in a registration database. Furthermore, in JapaneseLaid-open Patent Publication No. 2010-79448, there is proposed a fingervein authentication system which determines whether the preregisteredfinger vein pattern data is appropriate or not, and urges the user toperform a re-registration operation depending on the result of thedetermination. On the other hand, in Japanese Laid-open PatentPublication No. 2008-171094, there is disclosed a biometricauthentication apparatus which determines whether the biometricinformation presented for authentication is to be accepted or not, basedon the matching score between the presented biometric information andeach one of a plurality of biometric information templates, in order toreplace a selected one of the biometric information templates with theaccepted biometric information.

However, in any of these prior art methods, the registered biometricinformation is updated independently of cyclic environmental variationssuch as seasonal variations. Therefore, there can occur cases where theregistered biometric information representing the condition of the bodypart containing the biometric information acquired in a given season,for example, is updated by the biometric information acquired in adifferent season. As a result, if authentication is performed after acertain length of period has elapsed from the last update of theregistered biometric information, since the season at the time of theauthentication is different from the season at the time of theregistration, it follows that the biometric authentication apparatusperforms the authentication by using the registered biometricinformation representing the condition that is different from thecondition of the body part at the time of the authentication. This canresult in a degradation of authentication accuracy.

On the other hand, there is proposed a fingerprint matching system inwhich date/time information such as the time of day, day of week, anddate of year of registration is registered along with each fingerprintimage and, at the time of fingerprint matching, fingerprint imagesregistered within a specified date/time range are read out and used formatching (for example, refer to Japanese Laid-open Patent PublicationNo. 2001-229380).

SUMMARY

However, with the technique disclosed in Japanese Laid-open PatentPublication No. 2001-229380, the problem has been that the registeredbiometric information may have been affected by a factor other thancyclic environmental variations at the time of the registration, forexample, an incidental factor such as the skin surface being wet due towashing work. There has therefore been the possibility that theregistered biometric information selected at the time of matching mayrepresent the condition of the body part different from the condition ofthe body part containing the biometric information acquired in theenvironment at the time of matching.

According to one embodiment, a biometric authentication apparatus isprovided. The biometric authentication apparatus includes: a storageunit which stores representative matching data that represent featuresof biometric information of a registered user and that representconditions of a designated body part of the registered user, eachrepresenting one of at least two different portions of a variation rangeover which the condition of the body part containing the registereduser's biometric information varies due to cyclic environmentalvariations; a biometric information acquiring unit which generates abiometric image that represents biometric information of a user; amatching data generating unit which generates, from the biometric image,input matching data that represents the features of the biometricinformation of the user; a matching unit which matches the inputmatching data against at least one of the representative matching data;and an authentication judging unit which judges, based on a result ofthe matching, whether the user is to be authenticated as being theregistered user or not.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically illustrating the configuration of abiometric authentication apparatus according to a first embodiment.

FIG. 2 is a functional block diagram of a processing unit contained inthe biometric authentication apparatus.

FIG. 3 is a diagram illustrating one example of the relationship betweenthe seasonal variation of a body part containing biometric informationand the seasonal variation of a matching score computed for eachregistered matching data.

FIG. 4 is a diagram illustrating another example of the relationshipbetween the seasonal variation of the body part containing the biometricinformation and the seasonal variation of the matching score computedfor each registered matching data.

FIG. 5 is an operation flowchart illustrating a matching data updatingprocess.

FIG. 6 is an operation flowchart illustrating the matching data updatingprocess.

FIG. 7 is an operation flowchart illustrating a biometric authenticationprocess.

FIG. 8 is a diagram schematically illustrating the configuration of abiometric authentication apparatus according to a second embodiment.

DESCRIPTION OF EMBODIMENTS

Biometric authentication apparatus according to various embodiments willbe described below with reference to the drawings.

The biometric authentication apparatus registers in advancerepresentative matching data that represent the features of biometricinformation of each registered user and that represent the conditions ofa designated body part of the registered user, each representing one ofat least two different portions of the variation range over which thecondition of the body part containing the registered user's biometricinformation varies due to cyclic environmental variations. Then, thebiometric authentication apparatus computes input matching data from theinput biometric image acquired at the time of matching as representingthe user's biometric information, and compares the input matching datawith each representative matching data to determine whether the user isto be authenticated as being the registered user or not. Each time thematching process is performed for the registered user, the biometricauthentication apparatus obtains the matching score indicating thedegree of similarity between the input matching data and the matchingdata generated from the biometric image carrying the registered user'sbiometric information acquired at a designated time. Then, by referringto the temporal variation of the matching score, the biometricauthentication apparatus determines the representative matching data.

The cyclic environmental variations refer to the variations ofenvironmental parameters, such as temperature, humidity, etc., thataffect the body part containing the biometric information over arelatively long period ranging from several weeks to one or so years,exemplified by seasonal variations.

In the present embodiment, the biometric authentication apparatus uses apalm vein pattern as the biometric information for biometricauthentication. However, other kinds of biometric information, such asfingerprint or palm print, that may potentially be affected by cyclicenvironmental variations, and that can be presented in the form of astill image, may be used as the biometric information for biometricauthentication.

In this specification, the term “matching process” is used to refer tothe process for computing a matching score that indicates the degree ofsimilarity between input biometric information and registered biometricinformation. Further, the term “biometric authentication process” isused to refer to the entire authentication process which includes notonly the matching process but also the process for determining whetherthe user is an authenticated user or not by using the result of thematching process.

FIG. 1 is a diagram schematically illustrating the configuration of abiometric authentication apparatus according to a first embodiment. Asillustrated in FIG. 1, the biometric authentication apparatus 1 includesa display unit 2, an input unit 3, a biometric information acquiringunit 4, a communication unit 5, a storage unit 6, and a processing unit7. The display unit 2, input device 3, and biometric informationacquiring unit 4 may be provided separately from the cabinet containingthe communication unit 5, storage unit 6, and processing unit 7.Alternatively, the display unit 2, input device 3, biometric informationacquiring unit 4, communication unit 5, storage unit 6, and processingunit 7 may all be contained in a single cabinet, as in a so-callednotebook computer or a tablet-type terminal. The biometricauthentication apparatus 1 may further include a storage media accessdevice (not depicted) for accessing a storage medium such as a magneticdisk, a semiconductor memory card, or an optical storage medium. Then,the biometric authentication apparatus 1 may read out, via the storagemedia access device, a biometric authentication computer program storedon the storage medium and to be executed on the processing unit 7, andmay carry out the biometric authentication process in accordance withthe computer program.

The biometric authentication apparatus 1 generates by means of thebiometric information acquiring unit 4 a biometric image representingthe user's palm vein pattern, and carries out the biometricauthentication process by using the biometric image. When the user isauthenticated as being one of the registered users as a result of thebiometric authentication, the biometric authentication apparatus 1permits the user to use a host apparatus in which the biometricauthentication apparatus 1 is incorporated. Alternatively, the biometricauthentication apparatus 1 transmits to another apparatus (notdepicted), via the communication unit 5, a signal indicating that theuser has been authenticated, and permits the user to use that otherapparatus.

The display unit 2 includes a display device such as a liquid crystaldisplay. The display unit 2 displays a message indicating the body part(right hand or left hand) to be used for authentication or a guidancemessage for directing the user to place his hand properly on theposition where the biometric information acquiring unit 4 can correctlyacquire the biometric image. The display unit 2 also displays variouskinds of information associated with applications executed by theprocessing unit 7.

The input unit 3 includes, for example, a keyboard and a pointing devicesuch as a mouse. A command, data, user name, or user identificationnumber entered via the input unit 3 by the user is passed to theprocessing unit 7.

The biometric information acquiring unit 4 generates the biometric imagerepresenting the user's palm vein pattern. For this purpose, thebiometric information acquiring unit 4 includes, for example, atwo-dimensional array of imaging devices and an optical system. Theoptical system focuses an image of the body part placed within aprescribed distance of the surface of the biometric informationacquiring unit 4 onto the imaging device array so that the vein patterncan be captured in the biometric image without the user having to bringhis hand into contact with the biometric information acquiring unit 4.The biometric information acquiring unit 4 may further include anilluminating light source such as an infrared light-emitting diode forilluminating the user's hand. In the biometric image captured, thebrightness of the pixels representing the user's hand becomes higherthan the brightness of the other pixels in the image. Each time thebiometric image is generated, the biometric information acquiring unit 4transmits the biometric image to the processing unit 7.

The communication unit 5 includes a communication interface circuit forconnecting the biometric authentication apparatus 1 to a communicationnetwork (not depicted). The communication unit 5 transmits the usepermit granted to the user, or the result of the authentication receivedfrom the processing unit 7, to another apparatus via the communicationnetwork. Further, the communication unit 5 may acquire informationconcerning the environment, such as temperature or humidity, via thecommunication network, and may pass the information to the processingunit 7.

The storage unit 6 includes, for example, a nonvolatile semiconductormemory and a volatile semiconductor memory. The storage unit 6 stores anapplication program to be used in the biometric authentication apparatus1, the user name, user identification number, and personal settinginformation of at least one registered user, and various kinds of data.The storage unit 6 also stores a program for carrying out the biometricauthentication process. Further, for each registered user, the storageunit 6 stores representative matching data representing the features ofthe palm vein pattern of the left or right hand as the registeredbiometric information of the registered user. The representativematching data includes, for example, the positions or kinds of thefeature points representing the characteristic features, such as theendings or bifurcations of the veins, extracted from the biometric imagegenerated at the time of registration of the registered user or at thetime of updating of the representative matching data.

Alternatively, the representative matching data may be the biometricimage itself generated at the time of registration of the registereduser or at the time of updating of the representative matching data, ora portion of the biometric image.

In the present embodiment, at least two representative matching data arestored for each registered user. The representative matching data arethe matching data that correspond to the conditions representingdifferent portions of the variation range over which the condition ofthe body part containing the biometric information varies due to cyclicenvironmental variations. In the present embodiment, two representativematching data are stored, and each data represents the biometricinformation of the registered user at one of two end points of thevariation range that represents one of two portions into which thevariation range of the condition of the body part containing thebiometric information of the registered user has been divided. As willbe described later, at least one representative matching data continuesto be updated until the two representative matching data are eachupdated to represent the biometric information of the registered user atthe corresponding one of the two end points of the variation range ofthe condition of the body part containing the biometric information ofthe registered user. When the two representative matching data have beenupdated to represent the biometric information at the respective endpoints of the variation range of the condition of the body part, theupdating of the representative matching data is stopped. Then, therepresentative matching data after stopping the updating are held in thestorage unit 6. The updating of the representative matching data isperformed for each registered user.

The processing unit 7 includes one or a plurality of processors andtheir peripheral circuitry. The processing unit 7 acquires the biometricimage representing the user's biometric information from the biometricinformation acquiring unit 4, and carries out the biometricauthentication process by using the acquired biometric image. Further,the processing unit 7 carries out a registration process for registeringthe user as a registered user.

FIG. 2 is a functional block diagram of the processing unit 7. Asillustrated in FIG. 2, the processing unit 7 includes an orientationjudging unit 11, a matching data generating unit 12, a matching unit 13,an authentication judging unit 14, an updating unit 15, and aregistration unit 16. These units constituting the processing unit 7 arefunctional modules implemented by executing a computer program on theprocessor contained in the processing unit 7. Alternatively, these unitsconstituting the processing unit 7 may be implemented as firmware on thebiometric authentication apparatus 1.

Of these units constituting the processing unit 7, the orientationjudging unit 11 and the matching data generating unit 12 are used inboth the registration process and the biometric authentication process.The registration unit 16 is used in the registration process. On theother hand, the matching unit 13 and the authentication judging unit 14are used in the biometric authentication process. The updating unit 15is used in the biometric authentication process until the tworepresentative matching data of the registered user stored in thestorage unit 6 have come to represent the biometric information at therespective ends of the variation range over which the condition of thebody part containing the biometric information of the registered uservaries due to cyclic environmental variations. When the tworepresentative matching data of the registered user have been updated torepresent the biometric information at the respective ends of thevariation range, the updating unit 15 no longer need be used.

(Registration Process)

First, the registration process will be described.

Based on the biometric image generated by the biometric informationacquiring unit 4, the orientation judging unit 11 judges whether thebody part (in the present embodiment, the hand) containing the user'sbiometric information carried in the biometric image is orientedproperly to be processed in the matching process.

For example, the orientation judging unit 11 detects, from the biometricimage, a subject region which is the region on the biometric image thatcontains the body part (in the present embodiment, the hand) as thebiometric information. In the present embodiment, the value of any pixelcontained in the background region which is made up of pixels formingthe non-image region is lower than the value of any pixel contained inthe subject region. Therefore, the orientation judging unit 11 detects aset of pixels whose pixel values are not lower than a predeterminedthreshold value, and determines the set of such pixels as being a set ofsubject candidate pixels that may potentially represent the body partcontaining the user's biometric information. The orientation judgingunit 11 performs labeling on the set of subject candidate pixels, anddetermines that the region formed by connecting the subject candidatepixels is the subject region. The predetermined threshold value is, forexample, 10.

Whether the value of any pixel contained in the region representing theuser's hand is higher or lower than the value of any pixel contained inthe background region is determined by how the biometric informationacquiring unit 4 is configured.

Accordingly, when the value of any pixel contained in the regionrepresenting the user's hand is lower than the value of any pixelcontained in the background region, the orientation judging unit 11detects any pixel whose pixel value is lower than the threshold value asbeing a subject candidate pixel.

The orientation judging unit 11 obtains suitability judging metrics asmetrics for judging whether the orientation of the body part containingthe biometric information captured in the biometric image is suitable ornot. If any one of the suitability judging metrics indicates that theuser's hand captured in the biometric image is so small that it isdifficult to identify the details of the vein pattern, the orientationjudging unit 11 determines that the orientation of the body part is notsuitable. Further, if any one of the suitability judging metricsindicates that a portion of the hand containing the vein pattern to beused for matching is missing from the biometric image, the orientationjudging unit 11 determines that the orientation of the body part is notsuitable. On the other hand, if all the suitability judging metricsindicate that the vein pattern to be used for matching can be detectedfrom the user's hand captured in the biometric image, the orientationjudging unit 11 determines that the orientation of the body part issuitable.

In the present embodiment, the orientation judging unit 11 computes thearea and the center of the subject region as one example of thesuitability judging metric. The orientation judging unit 11 may compute,as another example of the suitability judging metric, the number ofpixels touching each image edge of the biometric image among the pixelscontained in the subject region. For example, if the center of thesubject region is located within a predetermined distance from one ofthe image edges of the biometric image, the orientation judging unit 11determines that the orientation of the body part is not suitable. Thepredetermined distance may be chosen to be, for example, one half of theaverage value of the width of the subject region on the biometric imagewhen the user's hand is placed in a suitable position relative to thebiometric information acquiring unit 4.

Further, if the difference between the number of pixels contained in thesubject region and touching one of the left and right edges of thebiometric image and the number of pixels contained in the subject regionand touching the other edge of the biometric image is not smaller than apredetermined threshold value, the orientation judging unit 11 maydetermine that the orientation of the body part is not suitable. Thepredetermined threshold value may be chosen to be, for example, onethird or one quarter of the vertical length of the subject region on thebiometric image.

Furthermore, if the area of the subject region is smaller than a minimumallowable area calculated by multiplying a reference area by apredetermined coefficient, the orientation judging unit 11 may determinethat the orientation of the body part is not suitable. The referencearea refers to the average area of the subject region on the biometricimage when the user's hand is placed in a suitable position relative tothe biometric information acquiring unit 4. The minimum allowable areacorresponds to the minimum area of the subject region at which thedetails of the vein pattern to be used for matching can be identified onthe biometric image, and may be chosen, for example, to fall within arange of values calculated by multiplying the reference area by 0.5 to0.8.

When it is determined that the orientation of the body part is notsuitable, the orientation judging unit 11 retrieves from the storageunit 6 a guidance message indicating the need to recapture the biometricinformation and directing the user to the correct position of the hand,and causes the display unit 2 to display the guidance message. Then, thebiometric information of the user is recaptured by the biometricinformation acquiring unit 4. The orientation judging unit 11 thenperforms the above-described process on the recaptured biometric image.On the other hand, when it is determined that the orientation of thebody part is suitable, the orientation judging unit 11 passes thebiometric image to the matching data generating unit 12 along with theinformation indicating the subject region. The information indicatingthe subject region may be, for example, a binary image having the samesize as the biometric image; in this binary image, the value of anypixel contained in the subject region is set, for example, to “1”, andthe value of any pixel contained in the background region is set, forexample, to “0”.

The matching data generating unit 12 generates matching datarepresenting the features of the biometric information contained in thebiometric image. For example, when the biometric authenticationapparatus performs the matching by minutiae matching, the matching datagenerating unit 12 extracts from the biometric image the feature points(referred to as minutiae) to be used for minutiae matching. Then, thematching data generating unit 12 generates the matching data by takingthe positions or kinds of the feature points.

For that purpose, the matching data generating unit 12 detects, fromwithin the subject region, a vein region made up of pixels representingthe veins and a non-vein region made up of pixels not representing theveins. In the present embodiment, the value of any pixel contained inthe vein region is lower than the value of any pixel contained in thenon-vein region. In view of this, the matching data generating unit 12binarizes the subject region so that the vein region is represented, forexample, by a set of pixels having pixel values not larger than a secondbinarization threshold value and the non-vein region by a set of pixelshaving pixel values larger than the second binarization threshold value.The second binarization threshold value is, for example, a predeterminedfixed value (for example, 150), or alternatively, it is set equal to theaverage pixel value of the pixels contained in the subject region or thevalue determined by applying discriminant analysis to the values of thepixels contained in the subject region.

Next, the matching data generating unit 12 applies, for example,thinning to the set of pixels having pixel values corresponding to theveins in the binarized subject region, and thereby generates a thinnedbinary image in which the veins are thinned. After that, the matchingdata generating unit 12 scans the thinned binary image by using aplurality of templates corresponding to the endings or bifurcations ofthe veins, and detects the position on the thinned binary image where itmatches one of the templates. Then, the matching data generating unit 12extracts the pixel at the center of the detected position as a minutia.

The matching data generating unit 12 may extract minutiae from thebiometric image by using any other known method that obtains veins'endings or bifurcations as minutiae. Further, the matching datagenerating unit 12 may obtain other feature quantities representing thefeatures of the vein pattern on the biometric image as the matchingdata. For example, the matching data generating unit 12 may divide thesubject region into a plurality of blocks, and may obtain datarepresenting the number of veins in each block as the matching data.

On the other hand, when the biometric authentication apparatus performsthe matching by pattern matching, the matching data generating unit 12may generate the matching data by taking the biometric image itself orby segmenting from the biometric image a region containing the veinregion on the biometric image. Further, the matching data generatingunit 12 may take as the matching data an image created by applyingprocessing such as edge enhancement or unevenness correction to theentire biometric image or a portion of the biometric image.

The matching data generating unit 12 passes the matching data to theregistration unit 16. When executing the biometric authenticationprocess, the matching data generating unit 12 passes the matching datato the matching unit 13.

The registration unit 16 acquires via the input unit 3 the user name ofthe user to be registered. Then, the registration unit 16 sets a useridentification number for uniquely identifying the user. Further, theregistration unit 16 sets the matching data received from the matchingdata generating unit 12 as initial matching data R0. Then, theregistration unit 16 creates two representative matching data R1 and R2by duplicating the initial matching data R0. The representative matchingdata R1 and R2 are each updated during the execution of the biometricauthentication process until the data comes to represent the biometricinformation at one or the other end of the variation range over whichthe condition of the body part containing the registered user'sbiometric information varies due to cyclic environmental variations.Then, the registration unit 16 stores the initial matching data R0 andthe two representative matching data R1 and R2 in the storage unit 6 asthe information for the registered user along with the user name anduser identification number. The user is thus registered as theregistered user in the biometric authentication apparatus 1.

(Biometric Authentication Process)

Next, a description will be given of the biometric authenticationprocess for determining whether the user is to be authenticated as beingthe registered user or not. In the present embodiment, the biometricauthentication apparatus 1 performs the biometric authentication processin accordance with the so-called one-to-one authentication method. Forthat purpose, during the execution of the biometric authenticationprocess, the processing unit 7 receives the input biometric image fromthe biometric information acquiring unit 4 and also receives via theinput unit 3 the user name or user identification number of the user tobe authenticated.

As in the registration process, the orientation judging unit 11 judges,based on the input biometric image, whether the orientation of the bodypart containing the biometric information of the user wishing to beauthenticated is suitable or not. If the orientation is not suitable,the orientation judging unit 11 instructs the biometric informationacquiring unit 4 to reacquire the input biometric image. Then, based onthe reacquired input biometric image, the orientation judging unit 11once again judges whether the orientation of the body part containingthe biometric information of the user is suitable or not. If theorientation of the body part is suitable, the matching data generatingunit 12 computes, from the input biometric image, input matching data Vwhich is the matching data representing the features of the user'sbiometric information. The matching data generating unit 12 passes theinput matching data V to the matching unit 13 and the updating unit 15.

The matching unit 13 that received the user name or user identificationnumber retrieves from the storage unit 6 the initial matching data R0and representative matching data R1 and R2 associated with theregistered user corresponding to the user name or user identificationnumber. The matching unit 13 then matches the user's input matching dataV against the initial matching data R0 and representative matching dataR1 and R2 associated with the registered user. Then, the matching unit13 obtains, as a result of the matching, a matching score that indicatesthe degree of similarity between the two matching data matched againsteach other; the matching score is computed for each of the initialmatching data R0 and representative matching data R1 and R2 associatedwith the registered user.

The matching unit 13 can perform the matching by using such techniquesas minutiae matching or pattern matching. The following describes howthe matching score S0 between the input matching data V and the initialmatching data R0 is computed. The matching scores S1 and S2 between theinput matching data V and the respective representative matching data R1and R2 are also computed in the same manner.

When using the minutiae matching, the matching unit 13 obtains thenumber of minutiae that match between the registered user's initialmatching data R0 and the user's input matching data V for the veinpattern. The matching unit 13 can then compute the matching score S0 bydividing the number of matching minutiae by the number of minutiaeextracted for the user's vein pattern. On the other hand, when using thepattern matching, the matching unit 13 computes normalizedcross-correlation values while changing the relative position betweenthe input biometric image as the matching data V and the biometric imagecontaining the registered user's vein pattern as the initial matchingdata R0. Then, the matching unit 13 determines the matching score S0 bytaking the maximum value of the normalized cross-correlation values.

The matching unit 13 obtains a maximum value Smax among the matchingscores S0, S1, and S2 computed for the respective matching data of theregistered user. The matching unit 13 passes the maximum value Smax ofthe matching score and the user identification number of the registereduser to the authentication judging unit 14.

Based on the result of the matching by the matching unit 13, theauthentication judging unit 14 judges whether the user is to beauthenticated as being the registered user or not. In the presentembodiment, if the maximum value Smax of the matching score is notsmaller than an authentication judging threshold value, theauthentication judging unit 14 determines that the biometric informationof the user matches the biometric information of the registered userdesignated for matching. Then, the authentication judging unit 14authenticates the user as matching the registered user. Afterauthenticating the user, the authentication judging unit 14 passes theresult of the authentication to the processing unit 7.

On the other hand, if the maximum value of the matching score is smallerthan the authentication judging threshold value, the authenticationjudging unit 14 determines that the biometric information of the userdoes not match the biometric information of the registered userdesignated for matching. In this case, the authentication judging unit14 does not authenticate the user. The authentication judging unit 14notifies the processing unit 7 of the result of the authenticationindicating the failure to authenticate the user. Then, the processingunit 7 causes the display unit 2 to display authentication resultinformation indicating the result of the authentication.

It is preferable to set the authentication judging threshold value tosuch a value that the authentication judging unit 14 succeeds toauthenticate the user only when the user is a legitimate registereduser. It is also preferable to set the authentication judging thresholdvalue to such a value that the authentication judging unit 14 fails toauthenticate the user when the user is a person other than a legitimateregistered user. For example, the authentication judging threshold valuemay be set equal to a value calculated by multiplying the differencebetween the maximum and minimum values that the matching score can takeby 0.7, and by adding the resulting product to the minimum value of thematching score.

The updating unit 15 updates the representative matching data R1 and R2of the registered user until the representative matching data R1 and R2come to represent the biometric information at the respective ends ofthe variation range over which the condition of the body part containingthe biometric information of the registered user varies due to cyclicenvironmental variations. Only when the user has been authenticatedsuccessfully, does the updating unit 15 update the representativematching data R1 and R2 by using the input matching data V obtained forthat user.

In the present embodiment, as long as the matching score S0 computed forthe initial matching data R0 continues to decrease, the updating unit 15continues to replace the representative matching data R1, R2 by theinput matching data V obtained when the user has been authenticatedsuccessfully. When the matching score reaches a minimum value, theupdating unit 15 takes the representative matching data R1, R2 as thematching data representing the biometric information of the registereduser at one end of the variation range over which the condition of thebody part containing the biometric information of the registered uservaries due to cyclic environmental variations.

FIG. 3 is a diagram illustrating one example of the relationship betweenthe seasonal variation of the body part containing the biometricinformation and the seasonal variation of the matching score computedfor each registered matching data. In the example illustrated in FIG. 3,it is assumed that the matching data of the registered user isregistered in spring and therefore that the condition of the body partcontaining the biometric information of the registered user at the timeof the registration is located near the center of the variation rangeover which the condition of that body part varies due to cyclic seasonalvariations.

In the graph depicted in the upper part of FIG. 3, the abscissarepresents the time (season), and the ordinate represents the conditionof the body part containing the biometric information of the registereduser. Curve 300 depicts how the condition of the body part containingthe biometric information of the registered user changes over time. Onthe other hand, in the graph depicted in the lower part of FIG. 3, theabscissa represents the time (season), and the ordinate represents thematching scores computed between the input matching data V and the threeregistered matching data R0, R1, and R2, respectively. Curve 310 depictshow the matching score S0 for the initial matching data R0 changes overtime. Curve 320 depicts how the matching score S1 for the matching dataR1 which is updated earlier than the matching data R2 changes over time.On the other hand, curve 330 depicts how the matching score S2 for thematching data R2 which is updated later than the matching data R1changes over time.

As depicted by the curve 300, as the summer approaches, the condition ofthe body part containing the biometric information of the registereduser approaches one end of the variation range of the condition of thatbody part. In the present embodiment, since the biometric information isthe palm vein pattern, the blood vessels expand as the summer approachesand the temperature rises. As a result, the difference between thecondition of the body part containing the biometric information of theregistered user at the time of the registration and the condition of thebody part containing the biometric information of the registered user atthe time of the biometric authentication becomes greater as the summerapproaches. Accordingly, as depicted by the curve 310, the matchingscore S0 for the initial matching data R0 continues to decrease with theapproach of summer. During this period, the representative matching dataR1 which is updated first is used for biometric authentication, and isupdated each time the biometric authentication is successfully done.Since the representative matching data R1 is updated to reflect thelatest condition of the body part containing the biometric informationof the registered user, the matching score S1 obtained for therepresentative matching data R1 exhibits a relatively high value, asdepicted by the curve 320. It is assumed that, at time d1, the conditionof the body part containing the biometric information of the registereduser reaches one end of the variation range. At time d1, the veinthickness becomes maximum as illustrated in the hand 350, and thematching score S0 for the initial matching data R0 reaches a minimum.After time d1, the difference between the condition of the body partcontaining the biometric information of the registered user at the timeof the initial registration and the condition of the body partcontaining the biometric information of the registered user at the timeof the biometric authentication gradually decreases, so that thematching score S0 for the initial matching data R0 changes fromdecreasing to increasing. As a result, after time d1, the representativematching data R1 is no longer updated. Then, at time d2 when it isconfirmed that the matching score S0 for the initial matching data R0reaches its minimum value at time d1, the updating unit 15 stopsupdating the representative matching data R1. In other words, therepresentative matching data R1 at time d1 is thereafter held in thestorage unit 6 as the matching data representing the biometricinformation of the registered user at one end of the variation rangeover which the condition of the body part varies due to cyclic seasonalvariations.

When the updating of the representative matching data R1 is stopped, theupdating unit 15 starts to update the other representative matching dataR2. From time d2 to time d3 when the difference between the condition ofthe body part containing the biometric information of the registereduser at the time of the initial registration and the condition of thebody part containing the biometric information of the registered user atthe time of the biometric authentication decreases to zero, the matchingscore S0 for the initial matching data R0 continues to increase.Accordingly, the representative matching data R2 is not updated untiltime d3. After passing time d3, the difference between the condition ofthe body part containing the biometric information of the registereduser at the time of the initial registration and the condition of thebody part containing the biometric information of the registered user atthe time of the biometric authentication begins to increase. As aresult, after time d3, the matching score S0 for the initial matchingdata R0 decreases, as depicted by the curve 330. Likewise, after timed2, the matching score S1 for the representative matching data R1constantly decreases. Accordingly, after time d3, the representativematching data R2 is updated by the input matching data V. Then, it isassumed that, at time d4 (for example, winter), the condition of thebody part containing the biometric information of the registered userreaches the other end of the variation range. At time d4, the veinthickness becomes minimum as illustrated in the hand 360, and thematching score S0 for the initial matching data R0 again reaches aminimum. After time d4, the difference between the condition of the bodypart containing the biometric information of the registered user at thetime of the initial registration and the condition of the body partcontaining the biometric information of the registered user at the timeof the biometric authentication gradually decreases, so that thematching score S0 changes from decreasing to increasing. The matchingscore S1 also changes from decreasing to increasing. As a result, aftertime d4, the representative matching data R2 is no longer updated. Then,at time d5 when it is confirmed that the matching scores S0 and S1 bothreach their minimum values at time d4, the updating unit 15 stopsupdating the representative matching data R2. In other words, therepresentative matching data R2 at time d4 is thereafter held in thestorage unit 6 as the matching data representing the biometricinformation of the registered user at the other end of the variationrange over which the condition of the body part varies due to cyclicseasonal variations.

FIG. 4 is a diagram illustrating another example of the relationshipbetween the seasonal variation of the body part containing the biometricinformation and the seasonal variation of the matching score computedfor each registered matching data. In the example illustrated in FIG. 4,it is assumed that the matching data of the registered user isregistered in summer and therefore that the condition of the body partcontaining the biometric information of the registered user at the timeof the registration is located at one end of the variation range overthe condition of that body part varies due to cyclic seasonalvariations.

In the graph depicted in the upper part of FIG. 4, the abscissarepresents the time (season), and the ordinate represents the conditionof the body part containing the biometric information of the registereduser. Curve 400 depicts how the condition of the body part containingthe biometric information of the registered user changes over time. Onthe other hand, in the graph depicted in the lower part of FIG. 4, theabscissa represents the time (season), and the ordinate represents thematching scores computed between the input matching data V obtained fromthe input biometric image at the time of the biometric authenticationand the matching data R0, R1, and R2 of the registered user,respectively. Curve 410 depicts how the matching score S0 for theinitial matching data R0 changes over time. Curve 420 depicts how thematching score S1 for the matching data R1 which is updated earlier thanthe matching data R2 changes over time. On the other hand, curve 430depicts how the matching score S2 for the matching data R2 which isupdated later than the matching data R1 changes over time.

As depicted by the curve 400, as the winter approaches, the condition ofthe body part containing the biometric information of the registereduser approaches the other end of the variation range of the condition ofthat body part. In the present embodiment, since the biometricinformation is the palm vein pattern, the blood vessels contract as thetemperature lowers. As a result, the difference between the condition ofthe body part containing the biometric information of the registereduser at the time of the registration and the condition of the body partcontaining the biometric information of the registered user at the timeof the biometric authentication becomes greater as the winterapproaches. Accordingly, as depicted by the curve 410, the matchingscore for the initially registered matching data continues to decreasewith the approach of winter. During this period, the representativematching data R1 which is updated first is used for biometricauthentication, and is updated each time the biometric authentication issuccessfully done. Since the representative matching data R1 is thusupdated to reflect the latest condition of the body part containing thebiometric information of the registered user, the matching score S1obtained for the representative matching data R1 exhibits a relativelyhigh value, as depicted by the curve 420. It is assumed that, at timed1, the condition of the body part containing the biometric informationof the registered user reaches the other end of the variation range. Attime d1, the matching score S0 reaches a minimum. After time d1, thedifference between the condition of the body part containing thebiometric information of the registered user at the time of theregistration and the condition of the body part containing the biometricinformation of the registered user at the time of the biometricauthentication gradually decreases, so that the matching score S0changes from decreasing to increasing. As a result, after time d1, therepresentative matching data R1 is no longer updated. Then, at time d2when it is confirmed that the matching score S0 reaches its minimumvalue at time d1, the updating unit 15 stops updating the representativematching data R1. That is, the representative matching data R1 at timed1 is thereafter held in the storage unit 6 as the matching datarepresenting the biometric information of the registered user at theother end of the variation range over which the condition of the bodypart varies due to cyclic seasonal variations.

When the updating of the representative matching data R1 is stopped, theupdating unit 15 starts to update the other representative matching dataR2. From time d2 to time d3 when the difference between the condition ofthe body part containing the biometric information of the registereduser at the time of the registration and the condition of the body partcontaining the biometric information of the registered user at the timeof the biometric authentication decreases to zero, the matching score S0for the initial matching data R0 continues to increase. Accordingly, therepresentative matching data R2 is not updated until time d3. Afterpassing time d3, the difference between the condition of the body partcontaining the biometric information of the registered user at the timeof the initial registration and the condition of the body partcontaining the biometric information of the registered user at the timeof the biometric authentication begins to increase. As a result, aftertime d3, the matching score S0 decreases, as depicted by the curve 430.Likewise, the matching score S1 also decreases. Accordingly, after timed3, the representative matching data R2 is updated. Then, it is assumedthat, at time d4 (for example, the hottest day), the condition of thebody part containing the biometric information of the registered userreaches the one end of the variation range which is nearer to thecondition at the time of the registration. At time d4, the matchingscore S0 again reaches a minimum. After time d4, the difference betweenthe condition of the body part containing the biometric information ofthe registered user at the time of the initial registration and thecondition of the body part containing the biometric information of theregistered user at the time of the biometric authentication graduallydecreases, so that the matching score S0 changes from decreasing toincreasing. As a result, after time d4, the representative matching dataR2 is no longer updated. Then, at time d5 when it is confirmed that thematching score S0 for the initial matching data R0 reaches its minimumvalue at time d4, the updating unit 15 stops updating the representativematching data R2.

It can be seen that, in the example illustrated in FIG. 4 as well as theexample illustrated in FIG. 3, the representative matching data R1 andR2 held after stopping the updating represent the condition of the bodypart containing the registered user's biometric information at therespective ends of its variation range. Since, after time d4, thevariation range of the condition of the body part is defined by therepresentative matching data R1 and R2, the initial matching data R0 maybe deleted from the storage 6 after the updating of both representativematching data R1 and R2 has been stopped.

FIGS. 5 and 6 are an operation flowchart illustrating the matching dataupdating process performed by the updating unit 15. The matching dataupdating process is carried out each time the biometric authenticationprocess is performed.

The updating unit 15 determines whether the updating of therepresentative matching data R1 has been stopped or not (step S101). Forexample, if an R1 update-stop flag which indicates that the updating ofthe representative matching data R1 has been stopped is stored in thestorage unit 6, the updating unit 15 determines that the updating of therepresentative matching data R1 has been stopped.

If the updating of R1 has not yet been stopped (No in step S101), theupdating unit 15 proceeds to determine whether the matching score S1obtained for the representative matching data R1 is smaller than thematching score S0 obtained for the initial matching data R0 (step S102).If the matching score S1 is not smaller than the matching score S0 (Noin step S102), then the updating unit 15 determines whether the currentupdating is the first updating for R1 (step S103). If it is the firstupdating (Yes in step S103), the updating unit 15 takes the matchingscore S0, obtained from the current cycle of the biometricauthentication process, as being the minimum value S0min of the matchingscore obtained for the initial matching data R0 at the current time(step S104).

After step S104, or after it is determined in step S103 that the currentupdating is not the first updating (No in step S103), the updating unit15 determines whether the condition for updating is satisfied or not(step S105).

The condition for updating is set in order to avoid the risk oferroneously replacing the matching data of the registered user with thematching data of some other user. The updating unit 15 determineswhether at least one of the following conditions is satisfied as thecondition for updating.

The maximum value of the matching score obtained from the current cycleof the biometric authentication process is higher than an update permitthreshold value which is higher than the authentication judgingthreshold value. The update permit threshold value is set, for example,equal to the authentication judging threshold value multiplied by 1.1 to1.2.

The difference between the matching score S1 obtained from the previouscycle of the biometric authentication process and the matching score S1obtained from the current cycle of the biometric authentication processis smaller than a predetermined threshold value. The predeterminedthreshold value is set, for example, equal to one hundredth of the rangeof values that the matching score can take.

The representative matching data R1 has been updated in at least one ofa predetermined number (for example, five) of most recently performedupdate cycles.

If the condition for updating is satisfied (Yes in step S105), theupdating unit 15 determines whether the matching score S0 obtained fromthe current cycle of the biometric authentication process is smallerthan the minimum value S0min of the previous matching score (step S106).If the matching score S0 is smaller than the minimum value S0min of theprevious matching score (Yes in step S106), the updating unit 15replaces the representative matching data R1 by the input matching dataV obtained from the current cycle of the biometric authenticationprocess. Further, the updating unit 15 replaces the minimum value S0minof the matching score by the matching score S0 (step S107). After stepS107, the updating unit 15 terminates the updating process.

On the other hand, if the condition for updating is not satisfied instep S105 (No in step S105), the updating unit 15 terminates theupdating process without updating the representative matching data R1.If, in step S106, the matching score S0 is not smaller than the minimumvalue S0min of the matching score (No in step S106), the updating unit15 also terminates the updating process without updating therepresentative matching data R1.

On the other hand, if it is determined in step S102 that the matchingscore S1 for the representative matching data R1 is smaller than thematching score S0 for the initial matching data R0 (Yes in step S102),the updating unit 15 stops updating the representative matching data R1(step S108). Then, the updating unit 15 stores in the storage unit 6,for example, the R1 update-stop flag indicating that the updating of therepresentative matching data R1 has been stopped. The representativematching data R1 now carries the matching data corresponding to the casewhere the matching score S0 exhibits a minimum value, i.e., the matchingdata representing the condition of the body part that most differs fromthe condition of the body part represented by the initial matching dataR0. It can therefore be deduced that the representative matching data R1represents the condition of the body part at one end of the variationrange over which the condition of the body part containing the biometricinformation varies due to environmental variations. Accordingly, bystopping the updating of the representative matching data R1 asdescribed above, the updating unit 15 can store in the storage unit 6the matching data representing the condition of the body part at one endof the variation range over which the condition of the body partcontaining the biometric information varies due to environmentalvariations. Further, a plurality of minima may appear in the matchingscore S0 due to such effects as noise or environmental variations (forexample, variations in weather and temperature). Therefore, the updatingunit 15 does not stop updating the representative matching data R1 untilthe matching score S1 becomes smaller than the matching score S0, i.e.,until the condition of the user's body part at the time of theauthentication comes to a condition intermediate between the conditionof the body part at the time of the initial registration and thecondition of the body part at one end of its variation range. In thisway, the updating unit 15 can properly locate the minimum value of thematching score S0.

As illustrated in FIG. 6, after step S108, or after it is determined instep S101 that the updating of R1 has been stopped (Yes in step S101),the updating unit 15 proceeds to determine whether the updating of therepresentative matching data R2 has been stopped or not (step S109). Forexample, if an R2 update-stop flag which indicates that the updating ofthe representative matching data R2 has been stopped is stored in thestorage unit 6, the updating unit 15 determines that the updating of therepresentative matching data R2 has been stopped.

If the updating of R2 has been stopped (Yes in step S109), the updatingunit 15 terminates the updating process.

On the other hand, if the updating of R2 has not yet been stopped (No instep S109), the updating unit 15 proceeds to determine whether thematching score S2 for the representative matching data R2 is smallerthan both the matching scores S0 and S1 obtained for the initialmatching data R0 and the representative matching data R1, respectively(step S110). If the matching score S2 is not smaller than the matchingscore S0 or S1 (No in step S110), then the updating unit 15 determineswhether the current updating is the first updating for therepresentative matching data R2 (step S111). If it is the first updating(Yes in step S111), the updating unit 15 takes the matching score S1 asbeing the minimum value S1min of the matching score obtained for therepresentative matching data R1 at the current time (step S112).

After step S112, or after it is determined in step S111 that the currentupdating is not the first updating (No in step S111), the updating unit15 determines whether the condition for updating is satisfied or not(step S113). The condition for updating R2 may be the same as thecondition for updating R1.

If the condition for updating is satisfied (Yes in step S113), theupdating unit 15 determines whether the matching score S1 obtained fromthe current cycle of the biometric authentication process is smallerthan the minimum value S1min of the previous matching score (step S114).If the matching score S1 is smaller than the minimum value S1min of theprevious matching score (Yes in step S114), the updating unit 15replaces the representative matching data R2 by the input matching dataV obtained from the current cycle of the biometric authenticationprocess. Further, the updating unit 15 replaces the minimum value S1minof the matching score by the matching score S1 (step S115). After stepS115, the updating unit 15 terminates the updating process.

On the other hand, if the condition for updating is not satisfied instep S113 (No in step S113), the updating unit 15 terminates theupdating process without updating the representative matching data R2.If, in step S114, the matching score S1 is not smaller than the minimumvalue S1min of the matching score (No in step S114), the updating unit15 also terminates the updating process without updating therepresentative matching data R2.

On the other hand, if it is determined in step S110 that the matchingscore S2 is smaller than both the matching scores S0 and S1 (Yes in stepS110), the updating unit 15 stops updating the representative matchingdata R2 (step S116). Then, the updating unit 15 stores in the storageunit 6, for example, the R2 update-stop flag indicating that theupdating of the representative matching data R2 has been stopped. Afterthat, the updating unit 15 terminates the updating process. Once stepS116 has been carried out, neither R1 nor R2 is thereafter updated inthe updating process because both the R1 update-stop flag and the R2update-stop flag are stored in the storage unit 6.

FIG. 7 is an operation flowchart of the biometric authentication processwhich is performed under the control of a computer program executed onthe processing unit 7.

As illustrated in FIG. 7, the processing unit 7 acquires from thebiometric information acquiring unit 4 the input biometric imagecontaining the biometric information of the user wishing to beauthenticated. Further, the processing unit 7 acquires from the inputunit 3 the user name or user identification number of the registereduser to be matched (step S201). Then, based on the position and size ofthe subject region of the body part containing the user's biometricinformation carried in the input biometric image, the orientationjudging unit 11 in the processing unit 7 judges whether the orientationof the body part is suitable or not (step S202). If the orientation ofthe body part is not suitable (No in step S202), the orientation judgingunit 11 retrieves from the storage unit 6 a guidance message indicatingthe need to recapture the biometric information and directing the userto the correct position of the hand, and causes the display unit 2 todisplay the guidance message. Then, the processing unit 7 returns tostep S201 to repeat the above process.

On the other hand, if the orientation of the body part is suitable (Yesin step S202), the matching data generating unit 12 in the processingunit 7 computes the input matching data V from the input biometric image(step S203). The matching data generating unit 12 passes the inputmatching data V to the matching unit 13 and updating unit 15 in theprocessing unit 7.

The matching unit 13 obtains a maximum value Smax from among thematching scores S0, S1, and S2 computed between the input matching dataV and the respective matching data R0, R1, and R2 of the registered usercorresponding to the input user name or user identification number (stepS204). Then, the matching unit 13 passes the maximum value Smax and theidentification number of the registered user to the authenticationjudging unit 14 in the processing unit 7. Further, the matching unit 13passes the matching scores S0, S1, and S2 to the updating unit 15.

The authentication judging unit 14 judges whether or not the maximumvalue Smax of the matching score is larger than or equal to theauthentication judging threshold value (step S205). If the maximum valueSmax of the matching score is smaller than the authentication judgingthreshold value (No in step S205), the authentication judging unit 14does not authenticate the user, and causes the display unit 2 to displaythe judging result (step S206). On the other hand, if the maximum valueSmax of the matching score is larger than or equal to the authenticationjudging threshold value (Yes in step S205), the authentication judgingunit 14 authenticates the user as being the registered user (step S207).Then, the updating unit 15 in the processing unit 7 carries out thematching data updating process (step S208).

After step S206 or S208, the processing unit 7 terminates the biometricauthentication process.

As has been described above, the biometric authentication apparatusregisters in advance, for each registered user, the representativematching data that represent the conditions of the registered user'sbody part, each representing two different portions of the variationrange over which the condition of the body part containing the biometricinformation varies due to cyclic environmental variations. Then, byperforming the matching process using the representative matching data,the biometric authentication apparatus can perform the matching processby using the matching data representing the condition close to thecondition of the body part presented for biometric authentication. Inthis way, the biometric authentication apparatus can suppress thedegradation of authentication accuracy caused by variations that canoccur in the condition of the body part containing the biometricinformation due to cyclic environmental variations. Further, asdescribed above, the biometric authentication apparatus stops updatingthe representative matching data after determining the representativematching data that represent the conditions each representing thecorresponding one of the two different portions of the variation rangeof the condition of the body part containing the biometric information.Therefore, even after some time has elapsed from the last update of therepresentative matching data, the biometric authentication apparatus canperform the matching process by using the matching data representing thecondition close to the condition of the body part presented forbiometric authentication.

Next, a biometric authentication apparatus according to a secondembodiment will be described. The biometric authentication apparatusaccording to the second embodiment updates or stops updating therepresentative matching data R1 and R2, based on the variations ofenvironmental parameters representing the environmental variations, forexample, climate data such as temperature or humidity, that may affectthe condition of the body part containing the biometric information.

FIG. 8 is a diagram schematically illustrating the configuration of thebiometric authentication apparatus according to the second embodiment.The biometric authentication apparatus 10 according to the secondembodiment includes a display unit 2, an input unit 3, a biometricinformation acquiring unit 4, a communication unit 5, a storage unit 6,a processing unit 7, and an environmental information acquiring unit 8.In FIG. 8, the component elements of the biometric authenticationapparatus 10 are designated by the same reference numerals as those usedto designate the corresponding component elements of the biometricauthentication apparatus 1 according to the first embodiment. Thebiometric authentication apparatus 10 of the second embodiment differsfrom the biometric authentication apparatus 1 of the first embodiment bythe inclusion of the environmental information acquiring unit 8 and inthe operation of the processing unit 7. The following descriptiontherefore deals with the environmental information acquiring unit 8 andthe processing unit 7.

At the time of the initial registration of the matching data, or eachtime the biometric authentication process is started, the environmentalinformation acquiring unit 8 acquires the environmental parametersrepresenting the environmental variations that may affect the conditionof the body part containing the biometric information. For example, ifthe environmental parameter is the temperature, the environmentalinformation acquiring unit 8 includes a temperature sensor, and if theenvironmental parameter is the humidity, the environmental informationacquiring unit 8 includes a humidity sensor. Each time an environmentalparameter acquisition request is received from the processing unit 7,the environmental information acquiring unit 8 acquires the requestedenvironmental parameter, for example, by measuring the ambienttemperature or humidity of the biometric authentication apparatus 10.The environmental information acquiring unit 8 passes the environmentalparameter to the processing unit 7.

Alternatively, the biometric authentication apparatus 10 may acquiresuch environmental parameters from another apparatus via a communicationnetwork. In this case, the communication unit 5 serves as anotherexample of the environmental information acquiring unit. Thecommunication unit 5 may then acquire as environmental parameters thehighest temperature, lowest temperature, highest humidity, or lowesthumidity measured on the day the matching data was initially registeredor on the day the biometric authentication process was executed.

The registration unit 16 in the processing unit 7 stores theenvironmental parameters acquired at the time of the initialregistration of the matching data in the storage unit 6 along with thematching data R0, R1, and R2. For convenience, the environmentalparameters associated with the matching data R0, R1, and R2 willhereinafter be designated as C0, C1, and C2, respectively.

In the matching data updating process illustrated in FIGS. 5 and 6, theupdating unit 15 in the processing unit 7 uses, instead of the matchingscores S0, S1, and S2, the absolute differences between theenvironmental parameters C0, C0, and C2 and the correspondingenvironmental parameters Cn acquired at the time of the execution of thebiometric authentication process. Then, in steps S104 and S107, theupdating unit 15 records the maximum value C0max of the absolutedifference |Cn-C0| between C0 and Cn, instead of recording the minimumvalue of the matching score S0. In step S106, the updating unit 15determines whether |Cn-C0| is larger than C0max and, if |Cn-C0| islarger than C0max, then updates the representative matching data R1while also updating the maximum value C0max. Further, when |Cn-C0|becomes smaller than |Cn-C1| in step S102, the updating unit 15 stopsupdating the representative matching data R1.

Likewise, in steps S112 and S115, the updating unit 15 records themaximum value C0max of the absolute difference |Cn-C1| between C1 andCn, instead of recording the minimum value of the matching score S1. Instep S114, the updating unit 15 determines whether |Cn-C1| is largerthan C0max and, if |Cn-C1| is larger than C0max, then updates therepresentative matching data R2 while also updating the maximum valueC0max. Further, when both |Cn-C0| and |Cn-C1| become smaller than|Cn-C1| in step S110, the updating unit 15 stops updating therepresentative matching data R2.

According to the above embodiment, the biometric authenticationapparatus can associate each representative matching data directly withthe value of the environmental parameter that affects the condition ofthe body part represented by that representative matching data.

According to a modified example of the second embodiment, theenvironmental parameters may be stored on a day-by-day basis in thestorage unit for one cyclic period of the cyclic environmentalvariations that affect the condition of the body part containing thebiometric information. Then, the registration unit may retrieve from thestorage unit the environmental parameters associated with the day of theregistration of the matching data, and may associate the retrievedparameters with the respective matching data R0, R1, and R2. Likewise,each time the matching data updating process is executed, the updatingunit may retrieve from the storage unit the environmental parametersassociated with the day of the execution of the updating process, andmay associate the retrieved parameters with the updated matching data.

According to another modified example of the second embodiment, thebiometric authentication apparatus may select from among the registeredmatching data the matching data to be used in the matching process byreferring to the information estimating the condition of the body partcontaining the biometric information. For example, the biometricauthentication apparatus may acquire, via the environmental informationacquiring unit, the environmental parameter at the time of the executionof the biometric authentication process as the information estimatingthe condition of the body part containing the biometric information.Then, the biometric authentication apparatus may select therepresentative matching data associated with the environmental parameterclosest to the acquired environmental parameter as the matching data tobe used in the matching process. The authentication judging unit thencompares the computed matching score with the authentication judgingthreshold value and, if the matching score is larger than theauthentication judging threshold value, then authenticates the user. Inthis modified example, since the matching unit computes the matchingscore only for the selected matching data, the biometric authenticationapparatus can reduce the amount of computation involved in the matchingprocess.

Further, according to a modified example of each of the aboveembodiments, the storage unit may store three representative matchingdata. For example, after stopping the updating of the representativematching data R1 and R2, the updating unit obtains the differencebetween the matching score S1 computed between the input matching data Vand the representative matching data R1 and the matching score S2computed between the input matching data V and the representativematching data R2. Then, the updating unit takes the input matching dataV as the third representative matching data R3 when the difference hasdecreased to a negligible level (for example, to one hundredth or lessof the maximum value that the matching score can take). In this case,the representative matching data R3 represents the biometric informationtaken at the center of the variation range over which the condition ofthe body part containing the biometric information varies due toenvironmental variations.

Further, the two representative matching data to be held in the storageunit need not necessarily be the matching data corresponding to therespective ends of the variation range of the condition of the body partcontaining the biometric information. Each representative matching dataneed only be made to represent the condition in one of the sub-rangesobtained by dividing the variation range of the condition of the bodypart containing the biometric information into the same number ofsmaller ranges as the number of representative matching data. Forexample, after obtaining the three representative matching data R1 toR3, as in the above modified example, the updating unit further obtainsthe difference between the matching score S1 computed between the inputmatching data V and the representative matching data R1 and the matchingscore S3 computed between the input matching data V and therepresentative matching data R3. Then, the updating unit takes the inputmatching data V as new representative matching data R4 when thedifference has decreased to a negligible level. The updating unitfurther obtains the difference between the matching score S2 computedbetween the input matching data V and the representative matching dataR2 and the matching score S3 computed between the input matching data Vand the representative matching data R3. Then, the updating unit takesthe input matching data V as new representative matching data R5 whenthe difference has decreased to a negligible level. In this case, therepresentative matching data R4 represents, for example, the conditionof the body part at a temperature located at the midpoint of the upperhalf section of the variation range of the temperature that varies dueto environmental variations, and on the other hand, the representativematching data R5 represents the condition of the body part at atemperature located at the midpoint of the lower half section of thevariation range of the temperature.

According to still another modified example, the biometricauthentication apparatus may perform the biometric authenticationprocess in accordance with the so-called one-to-many authenticationmethod. In this case, neither the user name nor the user identificationnumber for identifying the registered user is needed in the biometricauthentication process. The matching unit matches the input matchingdata against the representative matching data of all the registeredusers. Then, when the maximum value of the matching score is higher thanthe authentication judging threshold value, the authentication judgingunit authenticates the user as being the registered user correspondingto that maximum value. Then, the updating unit need only update therepresentative matching data for that registered user. In this case, thecondition for updating may be made stricter in order to prevent therepresentative matching data of the registered user from being replacedby the matching data of some other user than that registered user. Forexample, the update permit threshold value may be set equal to theauthentication judging threshold value multiplied by 1.3 to 1.4.

The biometric authentication apparatus and the biometric authenticationmethod disclosed in this specification are applicable to various kindsof apparatus or systems that perform biometric authentication betweenuser biometric information and preregistered biometric information inorder to permit the user to perform a desired operation. For example,the biometric authentication apparatus may be incorporated in anautomated teller machine or in an input apparatus for permitting entryto a room. Such apparatus or systems include, for example, a computersystem in which one or more terminals are connected to a server via acommunication network. In this case, each terminal is equipped with abiometric information acquiring unit, and the biometric informationacquired by the biometric information acquiring unit is transmitted tothe server. Then, the server carries out the biometric informationregistration or biometric authentication process by implementing thefunctions of the processing unit according to any one of the aboveembodiments.

Of the various functions incorporated in the processing unit accordingto each of the above embodiments, the processor of each terminal mayimplement the functions of the orientation judging unit and the matchingdata generating unit. On the other hand, the processor of the server mayimplement the functions of the matching unit, the authentication judgingunit, the updating unit, and the registration unit. This serves toalleviate the processing load on the server processor. A computerprogram having instructions for causing a computer to implement thevarious functions of the processing unit according to each of the aboveembodiments may be provided in the form recorded on a computer readablerecording medium such as a nonvolatile semiconductor memory, a magneticrecording medium, or an optical recording medium. However, the recordingmedium here does not include a carrier wave.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

What is claimed is:
 1. A biometric authentication apparatus comprising:a storage device configured to store first matching data for aregistered user, first representative matching data that is generatedbased on input matching data for a user obtained during a period whenthe degree of similarity between the input matching data and the firstmatching data is equal to or larger than a threshold value and secondrepresentative matching data that is generated based on the inputmatching data obtained during a period when the degree of similaritybetween the input matching data and the first matching data is largerthan the degree of similarity between the input matching data and thefirst representative matching data; a biometric sensor configured togenerate a biometric image that represents biometric information of auser; and a processor configured to generate, from the biometric image,the input matching data; match the input matching data against at leastone of the first and second representative matching data; and judge,based on a result of the matching, whether the user is to beauthenticated as being the registered user or not.
 2. The biometricauthentication apparatus according to claim 1, wherein the matching theinput matching data against at least one of the first and secondrepresentative matching data computes a first matching score thatindicates the degree of similarity between the first matching data andthe input matching data, and wherein the processor further configured toobtain a minimum value of the first matching score by examining temporalvariation of the first matching score computed each time the user isauthenticated as being the registered user, and take the input matchingdata corresponding to the minimum value as the first representativematching data.
 3. The biometric authentication apparatus according toclaim 2, wherein the storage device stores the first matching data andstores second matching data which is updated by the input matching data,and the processor further configured to, when the first matching scorecomputed for the input matching data obtained from the most recentbiometric image is smaller than the minimum value of the first matchingscore computed previously, replace the second matching data by the inputmatching data, and when the first matching score is larger than a secondmatching score that indicates the degree of similarity between the inputmatching data obtained from the most recent biometric image and thesecond matching data, take the second matching data as the secondrepresentative matching data.
 4. The biometric authentication apparatusaccording to claim 1, further comprising: an environmental informationacquiring device which, each time the input matching data is computed,acquires an environmental parameter representing the environment at thetime of the generation of the input matching data; and wherein theprocessor further configured to take, as the first or secondrepresentative matching data, the input matching data obtained from thebiometric image corresponding to a minimum value or a maximum value ofthe environmental parameter.
 5. The biometric authentication apparatusaccording to claim 1, wherein for each of the first and secondrepresentative matching data, the matching the input matching dataagainst at least one of the first and second representative matchingdata computes a matching score indicating the degree of similaritybetween the input matching data and the representative matching data,and the judging whether the user is to be authenticated or not judges,based on a maximum value of the matching score, whether the user is tobe authenticated as being the registered user or not.
 6. The biometricauthentication apparatus according to claim 1, wherein for each of thefirst and second representative matching data, the storage device storesa registered environmental parameter representing the environment at thetime of the generation of the biometric image used for the computationof the representative matching data, the matching the input matchingdata against at least one of the first and second representativematching data matches the input matching data against one of the firstand second representative matching data that corresponds to theregistered environmental parameter closest in value to the environmentalparameter representing the environment at the time of the generation ofthe biometric image, and computes a matching score indicating the degreeof similarity between the representative matching data and the inputmatching data, and the judging whether the user is to be authenticatedas being the registered user or not judges, based on the matching score,whether the user is to be authenticated as being the registered user ornot.
 7. A biometric authentication method comprising: generating, by abiometric sensor, a biometric image that represents biometricinformation of a user; generating, by a processor, from the biometricimage, input matching data for the user; matching, by the processor, theinput matching data against at least one of first and secondrepresentative matching data, the first representative matching databeing generated based on the input matching data obtained during aperiod when the degree of similarity between the input matching data andfirst matching data for a registered user is equal to or larger than athreshold value, and the second representative matching data beinggenerated based on the input matching data obtained during a period whenthe degree of similarity between the input matching data and the firstmatching data is larger than the degree of similarity between the inputmatching data and the first representative matching data; and judging,by the processor, based on a result of the matching, whether the user isto be authenticated as being the registered user or not.
 8. Thebiometric authentication method according to claim 7, wherein thematching the input matching data against at least one of the first andsecond representative matching data computes a first matching score thatindicates the degree of similarity between the first matching data andthe input matching data, and wherein the biometric authentication methodfurther comprises obtaining, by the processor, a minimum value of thefirst matching score by examining temporal variation of the firstmatching score computed each time the user is authenticated as being theregistered user, and taking, by the processor, the input matching datacorresponding to the minimum value as the first representative matchingdata.
 9. The biometric authentication method according to claim 8,wherein a storage device stores the first matching data and storessecond matching data which is updated by the input matching data, andwherein the biometric authentication method further comprises: when thefirst matching score computed for the input matching data obtained fromthe most recent biometric image is smaller than the minimum value of thefirst matching score computed previously, replacing the second matchingdata by the input matching data, and when the first matching score islarger than a second matching score that indicates the degree ofsimilarity between the input matching data obtained from the most recentbiometric image and the second matching data, taking the second matchingdata as the second representative matching data.
 10. The biometricauthentication method according to claim 7, further comprising: eachtime the input matching data is computed, acquiring, by an environmentalinformation acquiring device, an environmental parameter representingthe environment at the time of the generation of the input matchingdata; and taking, as the first or second representative matching data,the input matching data obtained from the biometric image correspondingto a minimum value or a maximum value of the environmental parameter.11. The biometric authentication method according to claim 7, whereinfor each of the first and second representative matching data of the atleast two different portions, the matching the input matching dataagainst at least one of the first and second representative matchingdata computes a matching score indicating the degree of similaritybetween the input matching data and the representative matching data,and the judging whether the user is to be authenticated or not judges,based on a maximum value of the matching score, whether the user is tobe authenticated as being the registered user or not.
 12. The biometricauthentication method according to claim 7, wherein for each of thefirst and second representative matching data, a storage device stores aregistered environmental parameter representing the environment at thetime of the generation of the biometric image used for the computationof the representative matching data, the matching the input matchingdata against at least one of the first and second representativematching data matches the input matching data against one of the firstand second representative matching data that corresponds to theregistered environmental parameter closest in value to the environmentalparameter representing the environment at the time of the generation ofthe biometric image, and computes a matching score indicating the degreeof similarity between the representative matching data and the inputmatching data, and the judging whether the user is to be authenticatedor not judges, based on the matching score, whether the user is to beauthenticated as being the registered user or not.
 13. A non-transitorycomputer-readable recording medium having recorded thereon a biometricauthentication computer program that causes a computer to execute aprocess comprising: generating, from a biometric image representingbiometric information of a user, input matching data for the user;matching the input matching data against at least one of first andsecond representative matching data, the first representative matchingdata being generated based on the input matching data obtained during aperiod when the degree of similarity between the input matching data andfirst matching data for a registered user is equal to or larger than athreshold value, and the second representative matching data beinggenerated based on the input matching data obtained during a period whenthe degree of similarity between the input matching data and the firstmatching data is larger than the degree of similarity between the inputmatching data and the first representative matching data; and judging,based on a result of the matching, whether the user is to beauthenticated as being the registered user or not.